Thaddaeus sits next to 4 phonetic neighbors — Theodore, Tobias, and Matthias are the closest matches by sound. Most share Thaddaeus's English-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"heart, courageous heart"
"Yahweh is God"
"cheerful, merry"
"bridge town"
"clearing in the forest"
"variant of Jason (Greek: healer) or Jayden (Hebrew: God has heard)"
"modern creative variant of Jason"
"foundation, steadfast one"
"wolf with a shield"
"open land, cleared field"
"thunder of God"
"son of God-peace"
"descendant of Bradan (salmon)"
"from the hay valley"
"modern invented name"
"lover of earth, earth-born"
"ancient, enduring"
"that which is believed"
"my lord"
"strength, honor"
"griffin (mythical creature symbolizing strength)"
Similar sound: These names share phonetic patterns with Thaddaeus — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Aramaic origins, giving them the same cultural heritage as Thaddaeus.
Rhythm: Thaddaeus is a 3-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.